Machine tool and pallet standby station

ABSTRACT

A machine tool and pallet standby station using a crane for changing a pallet between a table or pallet mounting table ( 27 ) of the machine tool and the pallet standby station are provided. The table ( 27 ) includes a plurality of guide pins ( 31 ) having tapered front ends, a plurality of elevatable lift pins ( 35 ) having spherical front ends, and a plurality of taper cones ( 37 ) having tapered outer peripheral surfaces. On the other hand, the pallet (P) includes at least two brackets ( 39 ) attached so as to project in the side directions from the two side surfaces of the pallet, and each bracket is formed with a guide hole ( 41 ) into which a guide pin ( 31 ) is inserted for rough positioning of the pallet. Further, the bottom of the pallet (P) is formed with a plurality of locate holes ( 45 ) having tapered inner peripheral surfaces and engaging with the spherical front ends of the lift pins for precision positioning of the pallet and a plurality of taper holes ( 47 ) having shapes complementary with the taper cones ( 37 ) and engaging with the taper cones for final positioning of the pallet.

TECHNICAL FIELD

The present invention relates to a machine tool and pallet standbystation using a crane to change pallets between a pallet mounting tableof a machine tool and a pallet standby station.

BACKGROUND ART

In a machine tool, when a workpiece finishes machining, the pallethaving the machined workpiece mounted thereon is dismounted from a tableor pallet mounting table of the machine tool and conveyed to a setupposition or other pallet standby station, while another pallet having asetup workpiece mounted thereon is mounted on the table of the machinetool, thereby changing pallets between the table of the machine tool andthe pallet standby station. Pallets are changed using an automaticpallet change system or manually by a worker using a crane etc. In eachcase, for good precision machining, the pallet has to be accuratelyarranged at a predetermined position on the table or pallet standbystation.

For such positioning, various methods may be used. For example, JapanesePatent Publication (B2) No. 8-18216 discloses a method of positioning apallet and a pallet support table in a pallet transfer system using astacker crane by making knock pins provided on the pallet support tableengage with holes provided in the bottom of the pallet. Further,Japanese Patent No. 3307477 discloses a method of making taper outerperipheral surfaces of front ends of a plurality of piston membersprovided on a table engage with a plurality of taper holes provided inthe bottom of a pallet for rough positioning and then making a pluralityof taper cones provided on the table and a plurality of taper holesprovided in the bottom of the pallet engage for main positioning.

On the other hand, installation of an automatic pallet change systemrequires a large space for at least the conveyance of pallets andtransfer of pallets. Therefore, when sufficient space cannot be secured,it is not possible to install an automatic pallet change system.Further, an automatic pallet change system requires a complicatedmechanism and is high in price, and therefore this is not suited tocases where costs have to be kept down. In this case, a worker manuallyoperates a crane etc. to hoist a pallet from the pallet standby stationand move it to above the table and to lower the pallet while arrangingthe pallet at a predetermined position on the table to thereby changepallets.

In this regard, the positioning method disclosed in Japanese PatentPublication (B2) No. 8-181216 and Japanese Patent No. 3307477 utilizesholes provided in the bottom of the pallets. Therefore, when a workermanually operates a crane to position a pallet, visual recognition ofholes is difficult and guiding the holes provided in the bottom of thepallet to the positions of pins on the table requires skill and takestime.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide a machinetool and pallet standby station enabling use of a manually operatedcrane to easily arrange a pallet at a predetermined position on amachine tool or pallet standby station.

According to the present invention, there is provided a machine toolhaving a pallet mounting table for placing a pallet thereon, wherein thepallet mounting table includes a plurality of guide pins having taperedfront ends, an elevatable lift pin having a spherical front end, and ataper cone having a tapered outer peripheral surface; the palletincludes at least two brackets provided on side surfaces of the palletso as to project in the side directions from two side surfaces of thepallet; each bracket is formed with a guide hole into which a guide pinis inserted for rough positioning of the pallet; and a bottom surface ofthe pallet is formed with a locate hole having a tapered innerperipheral surface and engaging with the spherical front end of the liftpin for precision positioning of the pallet and a taper hole having acomplementary shape with the taper cone and engaging with the taper conefor final positioning of the pallet.

In the machine tool according to the present invention, since the roughpositioning guide holes of the pallet are provided in the bracketsattached so as to project from the two side surfaces of the pallet, aworker can easily visually recognize the guide holes. Therefore, evenwhen using a manually operated crane to move a pallet, a worker caneasily guide the guide holes of the pallet to the guide pins on thepallet mounting table, so rough positioning of the pallet by a workerbecomes easy. Further, even if the position of a pallet is somewhat offfrom a horizontal position of the target position on the table, it iseasy to engage the spherical front end of the lift pin with the taperedinner peripheral surface of the corresponding locate hole of thepallets. If making these engage with each other, it is possible toprecisely arrange the pallet at the target position on the table.Further, since the taper cone on the table and the corresponding taperhole of the pallet are complementary in shape, the pallet is accuratelyarranged at the target position on the table if making these engage witheach other.

In the above machine tool, preferably, the pallet mounting table isprovided with an elevatable support pin having a flat front end surfaceand the bottom surface of the pallet is provided with a flat support pinabutting surface abutting against the flat front end surface of thesupport pin. By making this support pin and the corresponding supportpin abutting surface abut against each other, the pallet is heldhorizontal with respect to the top surface of the table and the effectis exhibited that engagement of the spherical front end of the lift pinand the tapered inner peripheral surface of the locate hole andengagement of the taper cone and the taper hole are facilitated.Further, when lowering the pallet, the support pin has a cushioningaction and a function to prevent damage to the lift pin and taper cone.

Further, preferably, the machine tool further includes a stopperabutting against the side surface of the pallet to stop the pallet at apredetermined position on the pallet mounting table. By making the sidesurface of the pallet abut against this stopper, it is possible todetermine the coordinates of the pallet along one axis in the horizontaldirection. By just making the pallet move in the other axial directionin the horizontal plane, it becomes possible to guide the guide holesover the guide pins.

There is provided a pallet standby station of a machine tool for placinga pallet thereon, which includes a plurality of guide pins havingtapered front ends at positions corresponding to guide holes of thepallet, an elevatable lift pin having a spherical front end at aposition corresponding to a locate pin of the pallet, and a taper conehaying a tapered outer peripheral surface at a position corresponding toa taper hole of the pallet. In this case, it similarly becomes possibleto accurately position a pallet on the pallet standby station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the overall configuration of amachining system using a machine tool and a standby station according tothe present invention.

FIG. 2 is a schematic view showing the overall configuration of amachine tool side of the machining system of FIG. 1.

FIG. 3 is a partial cross-sectional side view showing details of thepositioning structure of the pallet and table shown in FIG. 2.

FIGS. 4A to 4E are schematic views showing a positioning procedure of apallet and table in the machining system of FIG. 1.

FIG. 5 is a schematic view showing the overall configuration of thepallet standby station side of the machining system of FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will be described belowwith reference to the accompanying drawings.

Referring to FIG. 1, a machining system 11 using a machine tool and astandby station according to the present invention is comprised of amachine tool 13, a pallet standby station 15, and a pallet conveyancesystem for conveying a pallet P having a workpiece W mounted thereonbetween machine tool 13 and pallet standby station 15. Pallet standbystation 15 is the place for keeping a pallet P on standby for conveyanceto a pallet mounting table, that is, a table 27, of machine tool 13 andincludes a setup station for setup work including mounting workpiece Won pallet P and a table of a machine tool performing a previousmachining process.

The pallet conveyance system is comprised of a suspension type crane 17which is movable between machine tool 13 and pallet standby station 15and manually operated by a worker. However, the pallet conveyance systemneed only convey pallet P between machine tool 13 and pallet standbystation 15, and an automatically operated crane, automatic pallet changesystem, or other type of pallet conveyance system can be used as thepallet conveyance system.

As machine tool 13, for example, it is possible to use a machiningcenter. Referring to FIG. 2, machine tool 13 includes a bed 19 installedon a floor, a column 21 provided on bed 19, a spindle head 23 supportedby column 21, a spindle 25 supported rotatably on spindle head 23 andhaving a tool T mounted thereon, and a table 27 provided on bed 19. Inthe illustrated embodiment, column 21 can move on bed 19 in a Z-axisdirection (left-right direction in FIG. 1), spindle head 23 can move oncolumn 21 in a Y-axis direction (vertical direction in FIG. 1), andtable 27 can move on bed 19 in an X-axis direction perpendicular to theY-axis and Z-axis (direction vertical to paper surface in FIG. 1).However, machine tool 13 may also have another configuration and is notlimited to the illustrated embodiment.

On bed 19 of machine tool 13, a stopper 29 is provided, so that theZ-axis position of pallet P on bed 19 or table 27 is restricted bymaking the back surface (side surface) of pallet P moved by crane 17abut against stopper 29.

Next, referring to FIG. 3, the positioning structure for positioningpallet P on table 27 will be described in detail.

There are provided on table 27 a plurality of guide pins 31 extending inthe vertical direction and having tapered front ends, a plurality ofelevatable support pins 33 having flat front end faces, a plurality oflift pins 35 having spherical front ends and able to be elevatedindependent from support pins 33, and a plurality of fixed taper cones37 having tapered outer peripheral surfaces. Support pins 33 and liftpins 35 are elevated by for example cylinder devices and can be lockedin predetermined positions by lock devices. On the other hand, pallet Phas a plurality of L-shaped brackets 39 attached to two side surfaces ofpallet P in the longitudinal direction. The parts of L-shaped brackets39 projecting in the side directions from the two side surfaces orpallet P are formed with guide holes 41 into which guide pins 31 areinserted. Further, a bottom surface of pallet P is formed with flatsupport pin abutting faces 43 against which the flat front end faces ofsupport pins 33 abut, locate holes 45 having tapered inner peripheralsurfaces and engaging with spherical front ends of lift pins 35, andtaper holes 47 having complementary shapes with taper cones 37 andengaging with taper cones 37, corresponding to support pins 33, liftpins 35, and taper cones 37.

The positions of guide pins 31 are set so that pallet P is placed atgenerally the desired position on table 27 when guide pins 31 of table27 are inserted into guide holes 41 of pallet P. Guide pins 31 arepreferably different in lengths. Further, guide holes 41 preferably havediameters one size larger than guide pins 31. Note that, in theembodiment shown in FIG. 3, table 27 is provided with two guide pins 31,but three or more guide pins 31 may also be provided of course.

Further, the positions of support pin abutting faces 43, locate holes45, and taper holes 47 are determined so that support pin abuttingsurfaces 43, locate holes 45, and taper holes 47 of pallet P are opposedto corresponding support pins 33, lift pins 35, and taper cones 37provided on table 27 when guide pins 31 are inserted into correspondingguide holes 41 of pallet P. Furthermore, the front end faces of all ofsupport pins 33 are positioned in the same plane when support pins 33are at the highest elevated positions, while the front ends of all oflift pins 35 are positioned in the same plane when lift pins 35 are atthe highest elevated positions.

Table 27 is further provided with a pallet position confirmation system49 for confirming a relative position of the bottom surface of pallet Pwith respect to the top surface of table 27 and clamp devices 51 forclamping pallet P to table 27. In the embodiment shown in FIG. 3, palletposition confirmation system 49 includes a position detection rod 49 awhich is biased so as to project upward from the surface of table 27. Bydetecting the position of position detection rod 49 a when the front endof position detection rod 49 a contacts the bottom of pallet P and ispushed downward, it is detected that the top surface of table 27 and thebottom surface of pallet P are in a predetermined positionalrelationship. However, pallet position confirmation system 49 need onlyrecognize the relative position between the bottom surface of pallet Pand the top surface of table 27, and other types of contact typeposition detection systems, noncontact type position detectors usinglasers or magnetism, etc. may also be used as pallet positionconfirmation system 49. Further, in the embodiment shown in FIG. 3, eachclamp device 51 is comprised of a stud 51 a extending from the bottomcenter of taper hole 47 and having an enlarged front end and a hole 51 cformed at the center portion of taper cone 37 and having lock balls 51 binside it. When studs 51 a are inserted into holes 51 c, the enlargedfront ends of studs 51 a are locked by biased balls 51 b to therebyclamp pallet P on table 27. However, clamp devices 51 need only clamppallet P on table 27, and another structure may also be used. Further,in the embodiment shown in FIG. 3, clamp devices 51 are integrated withtaper cones 37 and taper holes 47, but they may also be providedseparately.

Next, referring to FIGS. 4A to 4E, the procedure for positioning palletP with respect to table 27 shown in FIG. 2 will be described.

At pallet standby station 15, a worker attaches a conveyor wire 53 to apallet P having a setup workpiece W mounted thereon, in order to enablepallet P to be suspended by crane 17. Next, the worker manually operatescrane 17 to hoist pallet P from pallet standby station 15 and move it toabove table 27 of machine tool 13. At this time, support pins 33 ontable 27 are elevated. Next, the worker manually operates crane 17 tolower pallet P and finely adjusting the horizontal position of crane 17while visually recognizing guide holes 41, thereby making guide pins 31of table 27 be inserted into guide holes 41 of pallet P. In this way,readily visible guide holes 41 are utilized for the rough positioning ofpallet P on table 27, and therefore pallet can be arranged so thatsupport pin abutting surfaces 43, locate holes 45, and taper holes 47are opposed to corresponding support pins 33, lift pins 35, and tapercones 37 without having to recognize the hard to see positions ofsupport pin abutting surfaces 43, locate holes 45, and taper holes 47 atthe bottom of pallet P.

In the pallet change system according to the present invention, guideholes 41 are formed on the parts, projecting in the side directions, ofbrackets 39 attached to the side surfaces of pallet P, and therefore theworker can easily recognize the positions of guide holes 41 andpositioning of guide holes 41 and guide pins 31 becomes easy. Further,since guide pins 31 have tapered front ends and guide holes 41 havediameters one size larger than guide pins 31, guide pins 31 can beeasily inserted into guide holes 41. Furthermore, in the case whereguide pins 31 are different in length, the front ends of guide pins 31differ in height. Therefore, it is possible to lower pallet P whileinserting guide pins 31 into corresponding guide holes 41 one by one,whereby insertion of guide pins 31 in guide holes 41 becomes furthereasier. In addition, before guide pins 31 are inserted into guide holes41, if the back surface of pallet P (rear side surface) is made to abutagainst stopper 29 provided on bed 19 of machine tool 13, the Z-axisdirection position of pallet P (that is, the position in the left-rightdirection in FIG. 2) is restricted, so that guide holes 41 can bepositioned above guide pins 31 by just making crane 17 move in theX-axial direction. Therefore, the crane operation becomes easier.

When the worker finishes inserting all of guide holes 41 of pallet Pover guide pins 31 of table 27, pallet P is further lowered and, asshown in FIG. 4B, flat support pin abutting surfaces 43 of pallet P ismade to abut against the flat front end surfaces of support pins 33 atthe elevated position. Due to this, pallet P is supported so that thebottom surface thereof extends parallel to the top surface of table 27.At this time, locate holes 45 and taper holes 47 are respectivelyseparated from lift pins 35 and taper cones 37 and not engaged withthem. Further, by placing pallet P on support pins 33, the impact at thetime pallet P contacts is absorbed by support pins 33 to prevent damageto lift pins 35 and taper cones 37. Note that, at this point of time,conveyor wire 53 is detached from pallet P, and crane 17 is moved fromabove machine tool 13 to a position not interfering with machining.

When pallet position confirmation system 49 confirms that pallet P islowered to a position where support pin abutting surfaces 43 of pallet Pabut against elevated support pins 33, as shown in FIG. 4C, theplurality of lift pins 35 are simultaneously elevated, the sphericalfront ends of lift pins 35 is engaged with the tapered inner peripheralsurfaces of locate holes 45 and pallet P is elevated to separate fromsupport pins 33. This being the case, the spherical faces of the frontends of lift pins 35 and the tapered inner peripheral surfaces of locateholes 45 cooperate with each other to accurately arrange pallet P at thedesired horizontal position. In this way, the pallet P is preciselypositioned.

When pallet position confirmation system 49 confirms that pallet P iselevated by lift pins 35 to a position where support pin abuttingsurfaces 43 of pallet P separate from support pins 33, as shown in FIG.4D, support pins 33 are lowered. Next, as shown in FIG. 4E, lift pins 35are lowered to make taper cones 37 on table 27 engage withcomplementarily shaped taper holes 47 of pallet P and accurately arrangepallet P at a desired position on table 27. At this time, pallet P isclamped at that position by clamp devices 51. In this way, pallet P isfinally positioned.

When pallet position confirmation system 49 confirms that pallet P islowered to the lowest lowered position, it is judged that the finalpositioning of pallet P has been completed and workpiece W on pallet Pis machined by machine tool 13. After this, when workpiece W finishesbeing machined, pallet P is elevated from table 27 to obtain the stateshown in FIG. 4B by a procedure reverse to the above. Conveyor wire 53is attached to pallet P to again enable pallet P to be hoisted by crane17, and then pallet P is moved to pallet standby station 15 or adownstream machining process. After workpiece W finishes being machined,it is also possible to use support pins 33 to lift pallet P from table27.

Next, referring to FIG. 5, the overall configuration or pallet standbystation 15 according to the present invention will be described.

Pallet standby station 15 includes a base 55 installed on the floor anda pallet pivot system 57 provided pivotably on base 55. Pallet pivotsystem 57 pivots 90 degrees about a pivot 58 between the position shownby the solid line in FIG. 5 and the position shown by the dotted line,so that an L-shaped pallet P can be moved between a horizontally laidstate (the state shown by the solid line in FIG. 5 where the long partis at the bottom) and a standing state (the state shown by the dottedline in FIG. 5 where the short part is at the bottom). Therefore, it ispossible to mount workpiece W on pallet P in safe position shown by thesolid line in FIG. 5 where there is no danger of workpiece W falling offpallet P and then make the pallet stand up by pallet pivot system 57 soas to support pallet P in a state where workpiece W is easy to machine.

Further, base 55 is provided with a pallet position measuring device 59for confirming that pallet P is arranged at a predetermined position onpallet pivot system 57 and a workpiece position measuring device 61 forconfirming that workpiece W is mounted at a predetermined position onpallet P. In the embodiment shown in FIG. 5, as pallet positionmeasuring device 59 and workpiece position measuring device 61, contacttype position detectors bringing pins into contact with the pallet orworkpiece and detecting the positions of the pins so as to measure theposition of the object are used, but noncontact type position detectionsystems using laser beams or magnetism may be used.

In pallet pivot system 57 of pallet standby station 15 as well, toaccurately arrange pallet P at a desired position, guide pins 63, liftpins, support pins, and taper cones similar to those of table 27 of FIG.3 are provided at positions corresponding to guide holes 41, support pinabutting surfaces 43, locate holes 45, and taper holes 47 of pallet P onthe part becoming the bottom in the state shown by the dotted line inFIG. 5. Note that, in FIG. 5, only a guide pin 63 is shown.

When positioning pallet P on pallet pivot system 57, pallet pivot system57 is pivoted to the position shown by the dotted line in FIG. 5, andthen the worker manually operates crane 17 so that guide pins 63 ofpallet pivot system 57 are inserted into guide holes 41 of pallet P.Since the rest of the procedure is similar to the case of positioningpallet P on table 27, the explanation thereof will be omitted. Further,since the action and effect of guide holes 41, support pin abuttingsurfaces 43, locate holes 45, and taper holes 47 of pallet P and guidepins 63, lift pins, support pins, and taper cones of pallet pivot system57 are similar to the action and effect between table 27 and pallet P,the explanation will be omitted.

1. A machine tool having a pallet mounting table for placing a palletthereon, wherein said pallet mounting table comprises a plurality ofguide pins having tapered front ends proximal to the pallet placed onthe pallet mounting table, an elevatable lift pin elevatable relative toa top surface of the pallet mounting table and having a spherical frontend proximal to the pallet placed on the pallet mounting table, and ataper cone having a tapered outer peripheral surface; said palletcomprises top and bottom surfaces and two brackets provided onrespective side surfaces of said pallet that join the top and bottomsurfaces such that the two brackets laterally project in respective sidedirections from a respective one of the side surfaces of the pallet;wherein each bracket is formed with a guide hole into which a respectiveone of the guide pins is inserted for rough positioning of said pallet;and wherein the bottom surface of said pallet is formed with a locatehole having a tapered inner peripheral surface and engaging with saidspherical front end of said lift pin for precision positioning of saidpallet, and is formed with a taper hole having a complementary shapewith said taper cone and engaging with said taper cone for finalpositioning of said pallet.
 2. The machine tool according to claim 1,wherein said pallet mounting table is provided with an elevatablesupport pin elevatable relative to the top surface of the palletmounting table and having a flat front end surface proximal to thepallet placed on the pallet mounting table, and the bottom surface ofsaid pallet is provided with a flat support pin abutting surfaceabutting against the flat front end surface of the support pin.
 3. Themachine tool according to claim 2, further comprising a stopper abuttingagainst a side surface of the pallet to stop said pallet at apredetermined position on said pallet mounting table.
 4. The machinetool according to claim 1, further comprising a stopper abutting againsta side surface of the pallet to stop said pallet at a predeterminedposition on said pallet mounting table.